Abstract: The present invention is in the technical field of synthetic biology and metabolic engineering. More particularly, the present invention relates to a method to determine the expression stability of a heterologous gene at a chromosomal location in a cell undergoing burden and to produce mutated cells or organisms transformed with a heterologous gene at a chromosomal location, wherein the expression of said heterologous gene is not influenced by a burden or wherein the expression of said heterologous gene is reduced by a burden. The present invention describes methods to locate interesting chromosomal knock-in locations in a cell. Such engineered cells and organisms are applied for the production of bioproducts, such as but not limited to carbohydrates, lipids, proteins, organic acids, amino acids, alcohols, antibiotics and peptides. Preferably, the invention is applied in the technical field of fermentation of metabolically engineered microorganisms.